Transcutaneous energy transfer systems

ABSTRACT

The present disclosure relates to an improved transcutaneous energy transfer (TET) system that generates and wirelessly transmits a sufficient amount of energy to power one or more implanted devices, including a heart pump, while maintaining the system&#39;s efficiency, safety, and overall convenience of use. The disclosure further relates one or more methods of operation for the improved system.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of the filing date of U.S.Provisional Patent Application No. 61/979,835 filed Apr. 15, 2014, thedisclosure of which is hereby incorporated herein by reference.

FIELD OF THE TECHNOLOGY

The present invention relates to transcutaneous energy transfer (TET)systems and methods of operation for such systems.

BACKGROUND

Transcutaneous energy transfer (TET) systems are used to supply power todevices such as pumps implanted internally within a human body. Amagnetic field generated by a transmitting coil outside the body cantransmit power across a cutaneous (skin) barrier to a magnetic receivingcoil implanted within the body. The receiving coil can then transfer thereceived power to the implanted pump or other internal device and to oneor more batteries implanted within the body to charge the battery.

Such systems should efficiently generate and wirelessly transmit asufficient amount of energy to power one or more implanted devices whilemaintaining the system's efficiency, safety, and overall convenience ofuse.

With respect to those systems' efficiency, one drawback suffered bypresent TET systems arises from the nature of the magnetic fieldgenerated by the transmitting coil. By its nature, the field extendsfrom the transmitting coil in every direction. As such, much of theenergy from the electromagnetic field emitted by the transmitting coilis not focused effectively or optimally at the receiving coil. Thislimits the efficiency (i.e., the coupling coefficient) of the wirelessenergy transfer. Another challenge arises from the fact that powerand/or current demands of an implanted device are not constant butrather subject to vary. As such, there is a need to efficientlyaccommodate such changes in power and/or current demand in order to mosteffectively power the implanted device.

With respect to convenience of the system, one challenge among presentTET systems arises from the difficulty in maintaining optimal axialalignment (in proximity to the surface of the patient's skin) and radialalignment (across the surface of the patient's skin) between thetransmitting and receiving coils to increase power transfer efficiencyand minimize transmitting coil losses that would result in heating.Firstly, a transmitting coil worn on the exterior of the body is subjectto shift in position, such as due to movement by the wearer. Moreover,once the transmitting coil is shifted out of place, repositioning thecoil, such as determining in which direction to move the coil in orderto reestablish alignment, may be difficult without some form ofguidance. As such, there is a need for a system that assists the wearerin positioning or repositioning the transmitting coil.

Further, a shift in the position of a transmitting coil worn on theexterior of the body also poses issues with respect to health and safetyof the system's wearer. If the coil shifts out of its proper alignmentwhile operating at full power, not only may the coupling coefficient ofthe power transfer be reduced, but it may cause unwanted overheating tothe wearer, and such overheating may be harmful to the skin orsurrounding tissue.

BRIEF SUMMARY OF THE INVENTION

One aspect of the present disclosure provides for a transcutaneousenergy transfer system, including: an internal component having apower-consuming device and an internal coil electrically connected tothe power-consuming device, the internal component being adapted formounting within the body of an animal; an external coil adapted formounting outside of the body; a current monitor operative to measurecurrent flow in the external coil and to provide an indication ofwhether or not the external coil is electromagnetically coupled to theinternal coil based on the measured current flow; and a drive circuitoperative to apply a power-level alternating potential to the externalcoil responsive to an indication from the current monitor that theexternal coil is electromagnetically coupled to the internal coil. Thedrive circuit may also be operative to apply a test-level alternatingpotential less than the power-level alternating potential to theexternal coil when the not applying the power-level alternatingpotential. The drive circuit may further be operative to ceaseapplication of the power-level alternating potential to the externalcoil in response to an indication from the current monitor that theexternal coil is not electromagnetically coupled to the internal coil.The drive circuit may yet further be operative to apply the test-levelalternating potential intermittently when the drive circuit is notapplying the power-level alternating potential. In further examples, thecurrent monitor may be operative to provide information representing adegree of coupling, and the drive circuit may be operative to apply thepower-level alternating potential when the degree of coupling exceeds athreshold value.

Another aspect of the present disclosure provides for a transcutaneousenergy transfer system including an internal component adapted formounting within the body of an animal, and an external component adaptedfor mounting outside of the body. The internal component includes aninternal coil, an internal device electrically connected to the internalcoil for receipt of power from the internal coil, and a telemetrytransmitter operative to send telemetry signals representing one or moreparameters relating to operation of the internal component. The externalcomponent includes an external coil, a telemetry receiver adapted toreceive the telemetry signals from the telemetry transmitter, a currentmonitor operative to measure current flow in the external coil and toprovide an indication of whether or not the external coil iselectromagnetically coupled to the internal coil based on the measuredcurrent flow, and a drive circuit operative in a normal mode ofoperation when the telemetry receiver receives the telemetry signals,and in a safe mode of operation when the telemetry receiver does notreceive the telemetry signals. The drive circuit may apply more power tothe external coil in the normal mode than in the safe mode. In the safemode, the drive circuit may apply an amount of power to the externalcoil sufficient to power the internal device and the telemetrytransmitter. In some examples, the drive circuit may be configured tooperate in the safe mode only when the telemetry receiver does notreceive the telemetry signals and the current monitor indicates that theexternal coil is inductively coupled to the internal coil. Also, in someexamples, the external coil, current monitor, and drive circuit may bedisposed within a common housing. Yet further, in some examples, thedrive circuit may be operative to drive the external coil so as tosupply at least about 20 watts of power to the internal device.

Yet another aspect of the disclosure provides for an implanted componentof a wireless energy transfer system, including: a secondary coil havinga secondary axis and a secondary conductor extending in a spiral aroundthe secondary axis; a secondary shield composed of a magnetizable,electrically insulating material extending transverse to the secondaryaxis in proximity to the secondary coil and to the rear of the secondarycoil; and a power-consuming device electrically connected to thesecondary coil. The secondary conductor may have inner and outer endsdisposed substantially on a common radial line perpendicular to thesecondary axis. The secondary shield may have a round hole extendingthrough it in alignment with the secondary axis. In some examples, theimplanted component may further include an implantable coil housinghaving a biocompatible exterior surface, containing the secondary coil,and having front and rear sides. A front side of the secondary coil mayface toward the front side of the coil housing. Additionally, the coilhousing may include one or more visually-perceptible indiciadifferentiating the front and rear sides of the housing.

Yet a further aspect of the disclosure provides for a driver for awireless energy transfer system, including: an external coil having aprimary axis and a primary conductor extending around the primary axis;a drive circuit operative to drive the external coil so that powerapplied to the external coil will be coupled to the internal coil; and ashield composed of a ferromagnetic or ferrimagnetic material havingelectrical conductivity less than about 0.3×10{circumflex over ( )}6 σand extending transverse to the primary axis, the shield including aplurality of plate-like segments arranged generally edge-to-edge withone another with gaps between edges of mutually adjacent segments. Insome examples, the shield may be composed of a ferrite. Also, in someexamples, at least some of the gaps may extend substantially radiallywith respect to the primary axis.

An even further aspect of the disclosure is directed to a driver for awireless energy transfer system including: a primary coil having aprimary axis and a primary conductor extending in a spiral around theprimary axis; a drive circuit operative to drive the primary coil; amain shield composed of a magnetizable, electrically insulating materialextending transverse to the primary axis in proximity to the primarycoil; and a shield wall composed of a magnetizable, electricallyinsulating material. The shield wall extends around the primary axis andprojects from a rear surface of the main shield facing away from theprimary coil, so that the shield wall and main shield cooperativelydefine a generally cup-like structure. At least a portion of the drivecircuit may be disposed within the shield wall.

In some examples, the drive circuit may further include one or morecapacitors connected in a resonant circuit with the primary coil and oneor more power semiconductors connected to the resonant circuit forsupplying power to the resonant circuit. The capacitors and powersemiconductors may be disposed within the shield wall.

One more aspect of the disclosure provides for a driver for a wirelessenergy transfer system including: a primary coil having a primary axisand a primary conductor extending in a spiral around the primary axis; adrive circuit operative to drive the primary coil; and a main shieldcomposed of a magnetizable, electrically insulating material extendingtransverse to the primary axis in proximity to the primary coil. Themain shield may have a hole extending through it in alignment with theprimary axis. The hole extending through the main shield may be square.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a transcutaneous energy transfer (TET)system in accordance with an aspect of the disclosure.

FIG. 2 is a schematic diagram of the power system circuitry for the TETsystem of FIG. 1 in accordance with an aspect of the disclosure.

FIG. 3 is a schematic diagram of the communication system circuitry forthe TET system of FIG. 1 in accordance with an aspect of the disclosure.

FIG. 4 is an exploded view of an external module of the TET system ofFIG. 1 in accordance with an aspect of the disclosure.

FIGS. 5A-5C. are top-down views of a printed circuit board, a shieldingelement, and an external wire coil included in the external module ofFIG. 4 in accordance with an aspect of the disclosure.

FIG. 6 is a schematic diagram of the implanted components of the TETsystem of FIG. 1 in accordance with an aspect of the disclosure.

FIG. 7 is an exploded view of an implanted coil module of the TET systemof FIG. 1 in accordance with an aspect of the disclosure.

FIGS. 8A and 8B are top down views of implementations of a circuit boardincluded in the implanted coil module of FIG. 7 in accordance withaspects of the disclosure.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a transcutaneous energy transfer (TET)system 100 used to supply power to an implanted therapeutic electricaldevice 102 in an internal cavity within the body, i.e., below the skinof a patient 104. The implanted electrical device 102 can include a pumpsuch as for use in pumping blood as a ventricular assist device (“VAD”),for example. The internal or implanted electrical device 102 can includecontrolling circuitry to control, for example, a pump.

As illustrated in FIG. 1, the TET system 100 includes both externalelectronics 120 mounted outside the body of the patient 104, as well asinternal or implanted electronics 150 mounted within the body of thepatient 104. The external electronics are electrically coupled to one ormore power sources, including, for example, an external battery 125 anda building power source 112 (such as AC power, or converted DC power,supplied from an electrical outlet in a building). The external powersources may supply an input voltage anywhere between about 20V and about250V. The external electronics 120 are also electrically coupled to anexternal primary coil 130, and the implanted electronics 150 areelectrically coupled to an internal or implanted secondary coil 140. Theexternal and implanted coils 130 and 140 are inductively coupled to oneanother through electromagnetic induction in order to transfer energywirelessly therebetween. In the example of FIG. 1, the external coil 130is housed in a common external module 110 together with the externalelectronics 120, whereas the implanted coil 140 and implantedelectronics 150 are not housed together.

The implanted electronics 150 are electrically coupled to an implantedbattery 155 and to the implanted electrical device 102. Energy receivedat the implanted coil 140 is stored in the implanted battery 155,provided to the implanted medical device 102, or both, via the implantedelectronics 150. Additionally, energy stored at the implanted batterymay be provided to the implanted medical device 102 via the implantedelectronics 150.

The external electronics 120 of the system 100 may include controlcircuitry 122, radio frequency (RF) telemetry circuitry 124, powersource selection circuitry 126, drive circuitry 128, and a userinterface 129. The power source selection circuitry 126 is configured toselect an external power source (e.g., battery 125, wall source 112)from which to provide power to the external coil 130. The drive circuit128 is configured to drive the external coil 130 such that energy istransferred from the external coil 130 to the implanted coil throughelectromagnetic induction. The control circuitry 122 is configured todetermine and execute instructions for controlling the power sourcecircuitry 126 and drive circuitry 128 in order to control the wirelesstransfer of energy between the external and implanted coils. Suchcontrol may include setting the pulse width and/or frequency oftransmission, controlling which power source is selected by the powersource circuitry 126, instructing the drive circuitry 128 to drive theexternal coil 130, etc. Determinations made by the control circuitry 120may be based on signals received from the telemetry circuitry 124,information received from external sensors 115, and/or inputs from theuser interface 129.

The implanted electronics of the system 100 may include implantedcontrol circuitry 152 and RF telemetry 154, as well as a rectifiercircuit 156, a voltage regulator circuitry 158, and power sourceselection circuitry 159. The rectifier circuit 156 may be configured toconvert AC power generated at the implanted coil 140 to DC power. Thevoltage regulator circuit is configured to adjust the voltage level ofthe converted DC power and power from the implanted battery 155 beforebeing provided to the implanted medical device 102. The implanted powerswitching circuitry 159 is configured to control whether the implantedmedical device 102 is powered from the implanted battery 155, theimplanted coil 140, or both. Similar to the purpose of the externalcontrol circuitry 122, the implanted control circuitry 152 may be usedto determine and execute instructions for controlling the voltageregulation settings of the voltage regulator circuitry 158, power sourceselections made by the implanted power switching circuitry 159, andoverall delivery of power to the implanted medical device 102. In someexamples, the implanted control circuitry 152 may further control anefficiency of the inductive coupling between the external and implantedcoils 130 and 140, such as by instructing an adjustment in the resonantfrequency of resonant circuit components 145 in the implanted coil 140.As with the external circuitry 120, such determinations at the implantedcircuitry may be based on RF telemetry 154 signals as well as otherinformation received from internal sensors 165.

The TET system 100 may optionally include a clinical monitor 160 forcollecting system parameters (e.g., implanted battery life, chargestored in implanted battery, alarms, etc.) to be monitored, such as bythe patient 104 or by a hospital clinical staff. The clinical monitormay include a memory, internal or external, for storing the collectedparameters, as well as for logging an event history of the patient 104(e.g., a low flow condition, a no-flow condition, an interrupt, etc.).The clinical monitor 160 may further be coupled to and receive/transmitinformation to and from units other than the TET system, such as to andfrom the patient's watch or smartphone, or to and from a hospitalcomputer database. The clinical monitor 160 may also be powered by itsown dedicated power source or battery 170.

In some examples, the clinical monitor 160, aside from receiving andmonitoring data from the other components of the TET system 100, maydeliver set points or parameters (e.g., a flow rate) pertaining to thedesired operation of the system 100. Such set points may be communicatedto the external electronics 120, implanted electronics 150, or both asan instruction for operating the system 100, and thereby utilized insetting further parameters of the system's operation, such as a pulsewidth and/or frequency for driving the wireless energy transmission topower the implanted medical device 102.

FIG. 2 schematically illustrates the power system circuitry of the TETsystem 100 of FIG. 1 for supplying power to the implanted medical device102. As shown in FIG. 2, the power source selection circuitry 126 of theexternal electronics 120 includes two inputs electrically coupled to theexternal battery 125 and building power source 112, respectively. Basedon instructions from the control circuitry 122, the power sourceselection circuitry 126 outputs power from one of the external powersources to an input of the drive circuit 128. The drive circuit 128amplifies the outputted power. The amplified power is then provided tothe external coil 130. The external coil is coupled to additionalcircuitry such as one or more capacitors 135 that form a resonantcircuit with the external coil. The capacitance may be between about 50nF and 200 nF. The external coil 130 generates a magnetic field whichinductively couples to the implanted coil 140 at the resonant frequencyof the resonant circuits.

As described above, the external power source selection circuitry 126may be controlled by the external control circuitry 122. For example, ifthe external control circuitry 122 determines that the externalelectronics 120 are not connected to a building power source 112, theexternal control circuitry 122 may instruct the external power sourceselection circuitry 126 to provide power to the external coil 130 fromthe external battery power source 125. For further example, if theexternal control circuitry 122 determines that the external electronics120 are connected to a building power source 112, the external controlcircuitry 122 may instruct the external power source selection circuitry126 to provide power to the external coil 130 from the building powersource 112 instead.

The driver circuitry 128 may also be controlled by the external controlcircuitry 122. For example, the external control circuitry 122 maydetermine an appropriate setting (e.g., voltage, current, pulse width)at which the external coil 130 should be driven so as to inductivelygenerate enough power at the implanted coil 140 that the implantedmedical device 102 may be supplied with a sufficient amount of power.The power requirements of the implanted device will depend on the natureof the device and also may vary during operation of the device. Forexample, systems for use with a typical VAD may be arranged to transmitat least 5 watts, at least 10 watts, at least 15 watts, or at least 20watts of continuous power to the implanted device 102.

At the implanted electronics 150, the rectifier circuitry 156 receivesthe AC power generated at the implanted coil 140, and rectifies the ACpower to provide DC power. The rectifier circuitry 156 may include adiode bridge, synchronous rectifier or other components known in the artfor AC-to-DC rectification. The DC output of the rectifier circuitry 156is then input to the voltage regulator circuitry 158, where it is cappedto a predefined voltage limit or threshold (e.g., 60V) by a voltagelimiter, e.g., breakdown diodes. The voltage is further conditionedusing a step-down DC to DC (DC-DC) converter 252, such as a buckswitching controller, single-ended primary-inductor converter (SEPIC),or other components known in the art, to a voltage and current levelrequired for powering the implanted medical device 102 (e.g., about18V). Optionally, in some systems, the order of the rectifier circuitryand the voltage regulator may be reversed. For instance, the DC-DCconverter may be replaced with a transformer used to convert the voltagelevel of the AC power, and the converted AC power may then be convertedto DC power by the rectifier circuitry. The output of the voltageregulator circuitry 158 is provided to one of the inputs of theimplanted power source selection circuitry 159. A second input of theimplanted power source selection circuitry 159 is electrically coupledto the implanted battery 155. In the example of FIG. 2, the implantedbattery 155 outputs a direct current that is coupled to an input of aDC-DC step-up or boost converter 254. The step-up converter 254conditions the voltage and current level of the power output by theimplanted battery 155 to a level required for powering the implantedmedical device 102. For example, the step-up converter 254 may raise thevoltage of the power output by the implanted battery 155 from about 12Vto about 18V. The implanted power source selection circuitry 159includes an output electrically coupled to the implanted medical device102.

The implanted power source selection circuitry 159 is configured toswitch between providing power to the implanted medical device 102 fromone of an implanted battery 155 and the implanted coil 140. In similarfashion to switching regulation of the external circuitry 120, suchinternal switching may be determined based on inputs provided to theimplanted control circuitry 152. Inputs to the implanted controlcircuitry 152 may also indicate an amount of voltage received at theimplanted coil 140, and a temperature of the implanted electronics 150.For instance, if the implanted control circuitry 152 determines that notenough energy is received at the implanted coil 140, or that thetemperature of one or more internal components is too high to safelyoperate, then the implanted control circuitry 152 may instruct theimplanted power source selection circuitry 159 to supply power to theimplanted medical device 102 from the implanted battery 155.

In addition to the circuitry for supplying power to the implantedmedical device, the implanted electronics 150 also includes chargingcircuitry 256 for charging the implanted battery 155 using the generatedwireless energy. The charging circuitry may be arranged so as to permitcharging the implanted battery 155 even while wireless energy issupplied to the implanted medical device 102. The charging circuitry 256may include one or more switches controlled by the implanted controlcircuitry 152.

In some examples, power provided to the implanted battery 155 may becontrolled so as to avoid constant discharging and recharging of theimplanted battery, (commonly referred to as “micro disconnects”) whichaffect the battery life of TET powered VAD systems, for instance due tofluctuations in power demands from the implanted medical device 102. Forexample, commonly owned U.S. Pat. No. 8,608,635, the disclosure of whichis hereby incorporated herein in its entirety, describes a TET systemthat dynamically adjusts the energy emitted by a transmitting coil basedon power demands of an implanted VAD.

FIG. 3 schematically illustrates communication circuitry for enablingcommunication among the electronic components of the TET system 100.Each of the dotted lines 312, 314 and 316 represents a wirelesscommunication channel between two of the components. Each of the solidlines 322, 324 and 326 represents a wired communication channel.

Beginning with the external electronics 120, the external electronicsare communicatively coupled to each of the external coil 130 (viachannel 322), external battery 125 (via channel 324), clinical monitor160 (via channel 312), and implanted electronics 150 (via channel 314).The external electronics 120 may be wired to those components with whichit shares a housing (e.g., in the present example, the external battery125, housed together in module 110), and are wirelessly coupled to theseparately housed components (e.g., in the present example, theseparately housed clinical monitor 160). Communication between theexternal electronics 120 and any implanted component (e.g., theimplanted electronics 150) is wireless.

In the example of FIG. 3, the sensors 115 associated with the externalelectronics are configured to measure each of the supply voltage andsupply current for the connected power sources, including the wall powersource 112 and the external battery power source 125. Additional sensorsare configured to measure an amount of current supplied to the externalpower source selection circuitry (126 in FIGS. 1 and 2), as well as thetemperature of the external coil 130 and associated electronics. Inaddition to these sensed values, the external electronics 120 mayreceive information signals from the implanted electronics 150indicating other values associated with the TET system 100, such as thevoltage and current at a load of the implanted coil 140, the voltage atthe implanted rectifier circuitry 156, etc.

Beyond accumulating data from communicatively coupled components andsensors 115/165, the external electronics 120 may also share gathereddata with other components of the TET system 100, such as with theclinical monitor 160 and implanted electronics 150. For example, theexternal electronics 120 may transmit all received and measured valuesto the clinical monitor 160 for further monitoring, logging, processingand/or analysis. Communication to the clinical monitor may beintermittent.

The implanted electronics 150 are responsible for gathering measuredsensor values and data of the implanted components of the TET system100. For instance, the implanted electronics 150 may receive informationregarding the voltage and current at a load of the implanted coil 140.As described above, this data may be relayed to the external electronics150 and/or clinical monitor 160 to further coordinate control andoptimize efficiency between the transmitter (external) and receiver(implanted) sides of the system 100.

The external electronics 120, implanted electronics 150, and clinicalmonitor 160 may all communicate by radio frequency telemetry moduleshaving RF transmitters and/or receivers, such as those modules describedin commonly owned U.S. Pat. No. 8,608,635. For example, the externalelectronics may communicate with the clinical monitor (via channel 312)using a medical Bluetooth communication channel. The implantedelectronics may communicate with the external electronics (via channel314) and clinical monitor (via channel 316) using a medical implantcommunication service (MICS).

One configuration of an external module 110 such as the module isdepicted in FIGS. 4 and 5A-5C. FIG. 4 illustrates an exploded view ofthe external module 110. The external module 110 contains each of theexternal electronics 120 and a primary coil (the external coil 130)disposed entirely within a carrying system or housing 405. Efficiency ofthe external module is improved by integrating the power electronics andprimary coil within a common housing. In TET systems having a separatelyhoused primary coil and drive electronics, the distance between the coiland drive electronics (often 1 meter) can result in cable losses andoverall weakness in the system. Co-locating the drive electronics andprimary coil eliminates such cable losses, and enables a high Q andhigher efficiency to be achieved.

In the example of FIG. 4, the housing 405 is made of a durablenon-conductive material, such as a plastic. The housing includes each ofan “outward-facing” cap 407 which faces away from the patient 104 and an“inward-facing” base 406 which faces towards the patient 104 when themodule 110 is in use. The cap 407 and base 406 may fasten to one anotherby any suitable fastening modality as e.g., press fitting, spin welding,ultrasonic welding, adhesive, etc. In the example of FIG. 4, the module110 is circular, although modules may take a different shape such as,e.g., square, oblong, etc. A thermal isolation layer 409 is integratedinto the base 406 of the housing 405, or added as an additional layer onthe surface of the inward facing side of the housing 405 to provide anadditional thermal barrier between the primary coil and the patient'sskin. The thermal isolation may be made of a polymer material (e.g.,silicone), and may provide a breathable surface for the skin pores ofthe patient.

The external electronics 120 are arranged on a printed circuit board 420(PCB) disposed near the “outward-facing” end of the module (e.g., withinthe cap 407) and extending transverse or perpendicular to a primary axisA of the module 110. The primary axis A extends in the outwarddirection, i.e., from the center of the base 406 to the center of thecap 407. The primary coil 430 is disposed near the opposite“inward-facing” end of the module (e.g., within the base 406). Such anarrangement ensures that the electronic components of the module do notinterfere with the inductive coupling between the external and implantedcoils 130 and 140 of the TET system 100.

The PCB 420 may be shaped to fit the housing 405 of the module 110. Inthe example of the circular module 110, the PCB 420 may be circular orannular in shape. FIG. 5A depicts a top down view of an annular shapedPCB 420 with a gap having a diameter between about 20 mm and about 35 mmin the center of the PCB 420, which lies on the primary axis A. Theelectronic circuit components, which may include one or more capacitors135 and other components coupled to the external coil 130 to form aresonant circuit, are arranged around the gap. The gap in the center ofthe PCB 420 permits or at least simplifies connection of the electroniccircuit components to the primary coil 130, although the gap may beomitted, such as from a circular PCB, and the primary coil 130 may beconnected via a different path. Also, as described in greater detailbelow, the PCB 420 includes connection points 436 and 438 to facilitateconnecting the primary coil 130 to the other electronic circuitcomponents.

The housing 405 of the module 110 may be wide enough to contain aprimary coil 130 with a diameter 70 mm or greater. For instance, thehousing of FIG. 4 has an outer diameter of about 90 mm or greater. Assuch, the PCB 420 may be wide enough to fit inside the housing 405without having to stack the capacitors physically above, or below, othercomponents disposed on the PCB. As shown in FIG. 5A, the capacitors 135may be disposed alongside the other circuitry on the PCB. In turn, thehousing of FIG. 4 may be made thinner (i.e., along the primary axis),relative to a smaller diameter housing of similar design. In the exampleof FIG. 4, the housing 405 may have a thickness (at the primary axis A)of between about 10 mm and 20 mm (e.g., 15 mm).

The primary coil 430 is a substantially planar coil comprised of asingle continuous conductor wire (e.g., Litz wire) wrapped in a planarspiral pattern around the primary axis A. As used in the presentdisclosure, the term “spiral” should be understood to include bothcurves that begin at the primary axis and wrap around the axis, as wellas curves that wrap around the axis beginning at a location radiallyapart from the axis, thereby leaving a gap or opening at the center ofthe coil. The coil 130 may be wrapped anywhere between 5 and 15 turns.Based on the given value ranges, and based the formula for calculatingair-core inductors L=(d{circumflex over ( )}2*n{circumflex over( )}2)/(18*d+40*1) (where d is the coil diameter, 1 is the coil length,and n is the number of turns in the coil), the coil 130 may have aninductance anywhere between 15 μH and 25 μH.

FIG. 5C depicts a top-down view of the primary coil 430. The conductorwire of the primary coil has an inner end 432 and an outer end 434. Inthe example of FIG. 5C, each of the wire ends 432 and 434 is disposedsubstantially at a common radial axis B extending radially from theprimary axis A. As shown in FIG. 4, each of the wire ends 432 and 434may curl upward and away from the plane of the coil 430 and towards thePCB 420. Each wire end may be soldered or otherwise connected to therespective connection points 436 and 438 on the PCB 420.

In order to shield the electronics of the PCB 420 from the magneticfield generated by the primary coil 130, the module 110 includes ashield 450 disposed between the PCB 420 and the primary coil 130. Theshield 450 includes an annular disc 453 centered at and extendingtransverse to the primary axis A, and pair of concentric rings 457 and458 defining a wall having a surface of revolution about the primaryaxis A and extending parallel to the primary axis A in the outwarddirection from the inner edge and outer edges of the annular disc 453,respectively.

The rings 457 and 458 may extend along the primary axis A for a lengthequal or greater than the height of the PCB 420 electronics such thatthe electronics (including the capacitors) are completely disposedwithin the semi-toroidal cavity formed by the shield 450.

Both the disc 453 and rings 457 and 458 are composed of a ferromagneticor ferrimagnetic material (e.g., a ferrite) having an electricalconductivity less than about _0.3×10{circumflex over ( )}6 o and arelative permeability of between about 2000 and about 12000. The disc453 may be a rigid plate having a thickness (in the primary axis Adirection) between about 1 mm and about 2 mm, and the rings 457/458 maybe made of a flexible foil, each having a thickness (in the radial axisB direction) between about 0.5 mm and about 1 mm. Other example modules(e.g., a module having a circular PCB with no gap) may include acircular shield with no hole in the center and a single ring extendingfrom the outer edge of the disc. In such an example, the PCB 420electronics (including the capacitors) may be completely disposed withinthe regular shaped cavity formed by the shield 450. Yet further examplesmay include a shield that is made from a single piece of ferromagneticor ferrimagnetic material and molded into a regular or semi-toroidalshape, depending on whether the module 110 includes a circular orannular PCB, respectively.

The shield 450 is disposed between the PCB 420 and the external coil 430along the primary axis A. The disc 453 of the shield 450 redirects orfocuses the magnetic field emitted from primary coil towards thesecondary coil 140 implanted within the patient. This focusing increasesthe coupling coefficient of the TET system 100, and further protects theelectronics of the PCB 420 from unwanted inductive coupling. The innerand outer rings 457 and 458 provide further protection, effectivelyguiding the magnetic field around (instead of through) the annular PCB420.

The disc 453 may be made up of multiple segments or sections. FIG. 5Billustrates a top-down view of a disc 453 having quarter segments502-508, although other discs may have a different number of segments(e.g., 2-8 segments). Each segment has a radius of between about 20 mmand about 35 mm. Gaps 512-518 are present between edges of mutuallyadjacent segments. The gaps 512-518 may be formed by cutting the discduring assembly, and may extend substantially radially from the primaryaxis A at the center of the disc 453. The gaps range from 0 mm to 0.5mm. In the example of FIG. 5B, each segment is about 1.5 mm thick (i.e.,along the primary axis A). Sectioning the disc 453 in the above manneris believed to improve efficiency of the TET system. At the center ofthe disc 453 is an internal hole 525. In the example of FIG. 5B, theinternal hole 525 is square, as such shape is believed to achieve anoptimal scatter field characteristic for coupling the primary andsecondary coils 130 and 140. The size of the internal hole 525 may rangefrom 20 mm to 35 mm, and in some examples may be shaped differently(e.g., circular, rectangular, triangular, etc.).

Each of the rings 457 and 458 may include a small slit (not shown) topermit passage of the primary coil wire through the rings in order toconnect the conductor wire ends 432 and 434 of the primary coil 430 tothe respective connection points 436 and 438 of the PCB 420. The innerwire end 432 at the inner perimeter of the primary coil 130 may passthrough the slit of the inner ring 457 to the inner connection point436, and the outer wire end 434 at the outer perimeter of the primarycoil 130 may pass through the slit of the outer ring 458 to the outerconnection point 438. The slits may be radially aligned with one anothersuch that the wire ends connect to the PCB 420 at substantially the samearea of the PCB 420. In an alternative example, the rings 457 and 458may not include slits and each wire end 432 and 434 may curl over andaround a respective ring on order to connect to the connection points436 and 438 of the PCB 420.

Also shown in FIG. 4 are spacers 440, disposed between the disc 453 andthe PCB 420. The spacers 440 provide sufficient distance between the PCB420 and the disc 453 in order to prevent possible shorting due to theconductivity of the disc 453. The spacers are preferably made from anon-conductive, non-magnetic, material such as plastic, and may have athickness between about 1 millimeter and about 10 millimeters (e.g.,about 6 millimeters thick). The example module of FIG. 4 depicts fourspacers, each spacer displaced over a respective segment 502-508 of thedisc 453. Other examples may include more or fewer spacers (e.g., 2spacers, 8 spacers, etc.).

Also shown in FIG. 4 at the outward facing side of the cap 407 is avisual indicator 480 including a plurality of light emitting diodes(LEDs) 481-486. As described below, the LEDs 481-486 are configured toindicate the position of the external primary coil 130 relative to animplanted secondary coil 140 and to further indicate a direction and/ordistance that the implanted coil 140 must be moved in order to betteralign with the implanted coil 140. The example module of FIG. 4 depictsa row of six LEDs, but other examples may other display technologiesknown in the art but also include more or fewer lights (e.g., 5 LEDs, 8LEDs, etc.), and the lights may be arranged in other configurations(e.g., a grid, a circle, etc.).

Turning now to the implanted components of the TET system 100, FIG. 6illustrates a schematic view of an example arrangement of the componentsimplanted within the patient 140. As shown in FIG. 6, each of theimplanted coil 140, the implanted battery 155, the implanted medicaldevice 102, and the implanted electronics 150 is disposed in a separatehousing and dispersed throughout the patient's body in order toaccommodate the anatomy of the patient. Each of the implanted coil 140,battery 155 and medical device 102 is electrically coupled to theimplanted electronics 150 via a separate electrical power cable.

As discussed above, the secondary coil 140 is inductively coupleable toa primary coil 130. Positioning of the secondary coil 140 within thepatient may be done in such a manner that makes mounting the externalmodule 110 in proximity to the secondary coil 140 easy for the patient.For instance, the secondary coil 140 may be positioned close to the skinof the patient. Moreover, the secondary coil 140 may be positioned closeto a relatively flat part of the patient's body to make mounting theexternal module 110 easier. In the example of FIG. 6, the secondary coil140 is positioned close to the front of the patient's chest, such thatmounting the external module 110 to the patient's chest is easy and putsthe external module 110 in close proximity to the secondary coil 140.

FIG. 7 illustrates an exploded view of an implanted coil module 700containing the secondary coil 140. As shown in FIG. 7, the secondarycoil 140 is disposed within a housing 705 of the module 700 having a cap710 and base 720 that fit together. Fitting the cap 710 and base 720together may be accomplished in any suitable manner known in the art,such as those described above in connection with the external module110, and may be the same or different as fitting the cap 408 and base406 of the external module 110. The housing 705 may be made of abiocompatible material with a dissipation factor suitable to avoidoverheating the module 700 or surrounding tissue. Preferably, thehousing does not increase more than about two degrees (° C.) due to heatgenerated from inductive charging between the primary coil 130 andsecondary coil 140.

Each of a circuit board 740 holding one or more capacitors 745 (e.g.,collectively acting as a high-voltage bulk capacitor), a shield 730, anda secondary wire coil 140 are disposed entirely within the housing 705,and extend transverse or perpendicular to a secondary axis C of themodule 700. The secondary axis C extends in the inward direction, i.e.,from the center of the base 710 to the center of the cap 720. Thesecondary coil 140 is preferably disposed proximate the base 720 of thehousing 705, which is adapted to be implanted closer to the skin of thepatient (and therefore closer to the external module 110), and the board740 with the capacitors 745 is preferably disposed proximate the cap 710of the housing 705 farther from the patient's skin. Additionally, thecap 710 and/or base 720 of the housing 705 may include one or morevisually perceptible indicia to indicate or differentiate which side ofthe housing 705 is front facing (i.e., the secondary coil 140 beingdisposed at that side) and which side of the housing 705 is rear facing(i.e., opposite the front facing side). The indicia aid implantation ofthe secondary coil module 800 in its proper orientation to maximize thecoupling coefficient between the external and secondary coils 130 and140.

The capacitors 745 are evenly distributed around the circuit board 740in order to distribute heat losses over a larger, more unified area.FIGS. 8A and 8B illustrate alternative arrangements of the circuit boardand capacitors. In FIG. 8A, the capacitors 745 are positioned at theouter perimeter 810 of a ring shaped circuit board 740 having an opening820 at the center. Each of the capacitors is electrically connected tothe ring via pins (e.g., 812, 814). In FIG. 8B, the capacitors 745 arepositioned in a circular pattern on a solid (no opening in the center)circuit board 740. Both arrangements permit for heat losses to be evenlydistributed due to the even distribution of the capacitors.

The shield 730 is disposed between the board 740 and the secondary coil140. As with the shielding 450 of the external module 110, the shield730 is beneficial both for shielding the board 740 from inductivecoupling, as well as improving the focusing of the magnetic fieldgenerated at the primary coil 130, thereby increasing the couplingcoefficient between the primary and secondary coils 130 and 140.

In the example of FIG. 7, the implanted coil 140 is a substantiallyplanar coil comprised of a single continuous conductor wire (e.g., Litzwire) wrapped in a spiral pattern around the secondary axis C. The coil140 may be wrapped anywhere between 5 and 15 turns, and may have adiameter substantially equal to the diameter of the primary coil 130,for example about 80 mm or more. The conductor wire may be electricallycoupled to the capacitors 745 at each of an inner wire end 742 and anouter wire end 744. In order to connect the wire ends 742 and 744 to thecapacitors 745, the ends may be curled upward and away from the plane ofthe coil 740 (which is transverse to the secondary axis C) and generallyaxially towards the board 740. Electrical connection between the wireends 742 and 744 and the capacitors 745 may be established by solderingeach wire end to a respective connection point 746 and 748 on the board740 holding the capacitors 745. As shown in FIG. 7, each of the wireends 742 and 744 and connection points 746 and 748 may be disposedsubstantially at a common axis D extending radially from the secondaryaxis C.

The board 740 may be annular shaped having a circular inner hole betweenabout 30 mm and about 70 mm in diameter (e.g., 17.5 mm), and a thickness(in the secondary axis C direction) of about 1 mm. As described above,the board 740 may include one or more capacitors 745 that are coupled tothe secondary coil 140, and having a capacitance of between about 100 nFand 150 nF. Together, the secondary coil 140 and capacitors 745 form aresonant circuit. The resonant circuit has a pair of load terminals(which may be the connection points 846 and 848) disposed within thehousing 705. In some examples, the board may optionally includeadditional circuitry for adjusting the resonant frequency of theresonant circuit, for instance through selective coupling of thecapacitors, and may also optionally include one or more temperaturesensors for monitoring the temperature of the implanted coil module 700.The board 740 of FIG. 7 is shown holding 9 capacitors in a ring, butother example boards, such as those of similar shape and size, may fitmore (e.g., 10) or fewer (e.g., 2 or 3) capacitors, and the capacitorsmay be arranged differently (e.g., in a grid).

Additionally shown in FIG. 7 is a port 715 built into both the cap 710and base 720 of the housing 705. The port is adapted to permit one ormore power cables or wires (not shown) to pass therethrough such thatthe cables or wires electrically connect the components disposed withinthe housing 705 to the implanted electronics 150. For instance, a cablehaving conductors may pass through the port 715 in order to electricallyconnect the load terminals disposed in the housing 705 to the implantedelectronics 150. It is preferable to include the capacitors 755 on theimplanted coil 140 side of the cable (i.e., in the implanted coil module700) to reduce the distance from the implanted coil 140 and the loadterminals. This in turn minimizes any power losses over the cable.Returning to FIG. 6, the implanted electronics 150 are electricallycoupled to, but housed separately from, the implanted coil 140. Theimplanted electronics 150 may separated between two or more circuitboards, such as a voltage rectifier board and control board. The voltagerectifier board would include the voltage rectifier circuit 156described above in connection with FIGS. 1 and 2, which rectifies ACpower generated at the implanted coil into DC power. The voltagerectifier board also would include the voltage regulator circuitry 158described above, which conditions the voltage supplied to the implantedmedical device 102 to a required level, as well as the implanted powersource selection circuitry 159 for switching between providing power tothe implanted medical device 102 from the implanted battery 155 and theimplanted coil 140.

The control board would include circuitry, such as a MOSFET inverter,responsible for driving the implanted medical device 102, as well as thecontrol circuitry 152 responsible for instructing a power sourceselection of the implanted power source selection circuitry 159. Thecontrol circuitry 152 may determine proper operation parameters of theimplanted coil 140 (e.g., a resonant frequency), and whether to powerthe implanted medical device 102 using energy from the implanted coil140, from the implanted battery 155, or both. The control board mayadditionally collect and communicate various data about the TET system100. For example, the control board may be configured to receive,interpret, store and/or relay information regarding the temperature ofthe power source selection circuitry 159. For further example, where theimplanted medical device 102 is an implantable pump, such as the VAD ofFIG. 7, the control board may be configured to handle informationtransmitted from sensors 165 at the pump, such as back-EMF exhibited bythe pump, and electrical current at the pump's stators. Storage of suchinformation may be done on a memory included on the control board, andthe information may be communicated to other components of the TETsystem 100, such as the external electronics 120 and the clinicalmonitor 160, using the RF telemetry circuitry 154 discussed above.

In an alternative embodiment, the voltage rectifier board and controlboard may be housed separately. In such examples, the cable extendingfrom the housing 705 of the implanted coil module 700 (described abovein connection to FIG. 7) electrically connects to an input terminal ofthe rectifier housing, and from there connects to an input terminal ofthe rectifier circuitry 156. As such, the rectifier circuit iselectrically coupled between the implanted coil 140 and the implantedmedical device 102 such that only load current passing from thecapacitors 845 passes along the conductors of the cable to the rectifiercircuitry 156 to the implanted medical device 102. In other examples,the voltage rectifier board and control board may be housed together,with the cable extending from the housing 705 of the implanted coil 140electrically connecting to an input terminal of the common housing.

The implanted battery 155 may be a cell lithium ion cell/battery housedwithin a titanium or medical grade plastic casing. In the case ofpowering a VAD, the battery may be configured to store charge betweenabout 12 volts and 16.8 volts. As stated above, the implanted battery iscoupled to the implanted medical device 102 in order to power theimplanted medical device 102 in response based on a determination by theimplanted control circuitry 152. The implanted battery 155 may also beelectrically coupled to the implanted coil 140 through the voltagerectifier board of the implanted circuitry 150 in order to temporarilystore power generated at the implanted coil 140 in excess of the powerneeded at the implanted medical device 102. That excess power may beused to charge the implanted battery 155 for later use in operating theimplanted medical device 102.

In an alternative embodiment to the example arrangement of FIG. 6, theimplanted coil may be disposed in a housing that is mounted to theimplanted medical device. For instance, FIG. 9 illustrates anperspective view of the implanted medical device 102 (which is in thisexample a ventricular assist device, or VAD, for assisting cardiacfunction of the patient) having an implanted coil housing 905 mounted toa flat end 902 of the VAD 102. The flat end 902 of the VAD 102 ispreferably positioned facing away from the heart and towards the chestof the patient, such that the implanted coil is positioned close to thepatient's skin. Further, the implanted coil housing 905 is preferablymounted such that the implanted coil 140 disposed therein faces towardsthe chest of the patient so that the coil shield is positioned betweenthe implanted coil and the VAD 102. This permits the implanted coil 140to be positioned proximate to an external module 110 mounted to thechest of the patient, maximizing coupling between the external andimplanted coils, while further shielding the magnetic components andconductive surfaces of the VAD from the electromagnetic TET field. Thealternative arrangement of FIG. 9 is also advantageous for providing aheat sink for the VAD. The implanted electronics are also mounted to VAD102. This makes implantation of the VAD and TET system significantlysimpler, since there are no additional device pockets and no cablingbetween the implanted coil housing 905, implanted electronics 907 andVAD 102.

The TET system collectively described above may include additionalfeatures further improving upon several aspects of the system'soperation. One such feature is the implementation of normal, start-up,and safe mode routines for operation, as well as testing routines fordetermining In which mode to operate. The testing routines provide forthe TET system 100 to drive the external coil 130 using differentamounts of current. Under normal mode operation, when the externalcomponents of the TET system 100 are in proper communication with theimplanted components, the drive circuitry 128 applies a power levelalternating potential (e.g., a maximum amount of current) to drive theexternal coil 130. As described above, under normal operation, the TETsystem may generate at least 5 watts, at least 10 watts, at least 15watts, or at least 20 watts of continuous power. This power may be usedto operate all power demands of the implanted medical device, RFtelemetry needs, primary and back-up electronic system requirements, andfurther to power to recharge the implanted battery. If, however, one ormore of the external components, such as the wireless energy transfercoils or RF telemetry coils, are not in properly coupled with one ormore corresponding implanted components, less current may be applied todrive the external coil 130. The amount of reduction of the current maybe based on the particular component or components that are not properlycoupled.

The start-up routine may determine between operating the TET system 100in one of the start-up and normal modes, and may be controlled by theexternal control circuitry 122. In the start-up routine, the TET system100 may begin in start-up mode by applying a test-level alternatingpotential to drive the external coil 130 in order to test the degree ofcoupling between the external coil 130 and the implanted coil 140. Thetest-level alternating potential generates enough power to sense animplanted system or coil, but not enough power to operate the implanteddevice. For example, the test-level alternating potential may generateabout 250 mW or less. The sensors 115 of the external control circuitry122 may include a coupling detection circuit operative to detect thedegree of inductive coupling between the external coil 130 and theimplanted coil 140. This detection may be performed at least in partusing a current monitor to measure the current flow in the external coil130. Information regarding the detected coupling may then provided fromthe coupling detection circuit to the external control circuitry 122.The external control circuitry 122 may then determine, based on theprovided coupling information, whether to continue in start-up mode ortransition to normal mode.

If the external control circuitry 122 is in normal mode and does notreceive an indication (or otherwise determines) that the external andimplanted coils 130 and 140 are properly coupled, the external controlcircuitry 122 may instruct the drive circuitry 128 to cease applicationof the power-level alternating potential to drive the external coil 130,and may further transition to start-up mode and apply the test-levelalternating potential to the external coil 130. The test-levelalternating potential may be applied intermittently to determine whetherthe external and implanted coils 130 and 140 are properly orsufficiently coupled. The test-level alternating potential may providesufficient current to determine the presence of inductive couplingwithout generating a magnetic field strong enough to harm the patient(such as overheating the skin or tissue of the patient) despite the lackof inductive coupling between the external and implanted coils 130 and140. Additionally, the test-level alternating potential avoidsunnecessary expenditure of power, while still enabling the externalcontrol circuitry 122 to continue monitoring and evaluating the couplingbetween the coils 130 and 140.

In the safe-mode routine, the level of wireless power transmitted may bedetermined based on whether the RF telemetry circuits of the externaland implanted electronics 124 and 154 are properly communicating withone another. For example, if the external control circuitry 122determines that a receiver of the external RF telemetry circuitry 124 isnot receiving RF telemetry signals from a transmitter of the implantedRF telemetry circuitry 154, then the external control circuitry 122 mayinstruct the drive circuitry 128 to apply a relatively low power-levelalternating potential to the external coil 130. In other words, thedrive circuitry 128 would apply less current (a shorter pulse width) tothe external coil 130 in the safe mode as compared to a normal mode ofoperation. The low power-level alternating potential would be strongenough to drive the external coil 130 to generate enough power tooperate the implanted medical device 102. For example, with respect to aVAD, the power needs of the VAD may be defined by the blood flow needsof the patient (which in turn may be programmed by clinical staff). Suchpower needs can range from about 2 watts to about 5 watts.

The external control circuitry may be configured to implement bothstart-up and safe mode routines. Under such conditions, the drivecircuit 128 may be operative to apply the low power-level alternatingpotential to the external coil 130 only if the coupling detectioncircuitry determines that the coils are properly coupled, and theexternal control circuitry determines that the external RF telemetrycircuitry 124 is not receiving RF telemetry signal from the implantedelectronics.

Another feature of the TET system is an alignment protocol for aiding auser in properly aligning the external and implanted coils in order tomaximize efficiency of energy transfer therebetween.

The external control circuitry 122 may determine the then-present degreeof coupling between the external and implanted coils 130 and 140 basedon received information from the sensors 115. The information may bereceived in the form of input signals. One such signal may be providedby a voltage or current monitor coupled to the external coil 130, andmay indicate an amount of voltage and/or amount of current at theexternal coil 130. Another such signal may be provided by the externalRF telemetry circuitry 124 and may be indicative of power transfer(e.g., a coupling coefficient, or a current efficiency) between thecoils. The telemetry signal may be received from the implanted RFtelemetry circuitry 154, which itself is coupled to an implanted sensor165 that measures current in the implanted coil 140.

The external control circuitry 122 alerts the patient as to the degreeof coupling between the external and implanted coils 130 and 140.

Such alerts may be conveyed visually, such as by activating a humanperceptible signal, such as with visual or aural indicator. In theexample of the visual indicator, the indicator may include a number oflights or LEDs (e.g., the LEDs 481-486 on the outward facing cap 407 ofthe external module 420 of FIG. 4). For example, the number of lightsactivated may indicate the degree of coupling. The number of lightsactivated for any given degree of coupling may be preconfigured, forinstance such that the greater the degree of coupling, the more (oralternatively, the fewer) lights that are activated.

The above disclosure generally describes a TET system for use in a userhaving an implanted VAD. Nonetheless, the disclosure is similarlyapplicable to any system having a transcutaneous stage of wireless powerdelivery. As such, the disclosure is similarly applicable for drivingany power-consuming device implanted in any human or other animal (e.g.,hearing aids, pacemakers, artificial hearts, etc.).

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1.-2. (canceled)
 3. A transcutaneous energy transfer system comprising:(a) an internal component adapted for mounting within the body of ananimal, the internal component including: an internal coil; an internaldevice electrically connected to the internal coil for receipt of powerfrom the internal coil; and a telemetry transmitter operative to sendtelemetry signals representing one or more parameters relating tooperation of the internal component; and (b) an external componentadapted for mounting outside of the body, the external componentincluding: an external coil; a telemetry receiver adapted to receive thetelemetry signals from the telemetry transmitter; a current monitoroperative to measure current flow in the external coil and to provide anindication of whether or not the external coil is electromagneticallycoupled to the internal coil based on the measured current flow; and adrive circuit operative in a normal mode of operation when the telemetryreceiver receives the telemetry signals, and in a safe mode of operationwhen the telemetry receiver does not receive the telemetry signals, thedrive circuit being operative in both the normal and safe modes to applypower to the external coil so that power applied to the external coilwill be coupled to the internal coil, the circuit being operative tocontrol the power applied to the external coil at least in partresponsive to the telemetry signals when operating in the normal mode.4. The system as claimed in claim 3, wherein the drive circuit isoperative to apply more power to the external coil in the normal modethan in the safe mode.
 5. The system as claimed in claim 3, wherein thedrive circuit is operative, in the normal mode, to apply an amount ofpower to the external coil sufficient to power the internal device andthe telemetry transmitter.
 6. The system as claimed in claim 3, furthercomprising a coupling detection circuit operative to provide anindication of whether or not the external coil is electromagneticallycoupled to the internal coil, wherein the drive circuit is configured tooperate in the safe mode only when the telemetry receiver does notreceive the telemetry signals and the coupling detection circuitindicates that the external coil is inductively coupled to the internalcoil.
 7. The system as claimed in claim 3, wherein the external coil,current monitor, and drive circuit are disposed within a common housing.8. The system as claimed in claim 3, wherein the drive circuit isoperative to drive the external coil so as to supply at least about 20watts of power to the internal device. 9.-18. (canceled)